Conventionally, raw materials for the main soft segment of a polyurethane produced on an industrial scale are classified into an ether type typified by polytetramethylene glycol, a polyester polyol type typified by an adipate-based ester, a polylactone type typified by polycaprolactone, and a polycarbonate type typified by polycarbonate diol (Non-Patent Document 1).
On the other hand, a polyurethane using a polycarbonate type typified by polycarbonate diol is considered to be of the best durability grade in terms of heat resistance and hydrolysis resistance and is widely used as a durable film, an artificial leather for cars, an (aqueous) paint, and an adhesive.
Although the polycarbonate diol widely available on the market at present is mainly a polycarbonate diol synthesized from 1,6-hexanediol, due to high crystallinity thereof, a polyurethane formed has a problem that the cohesion of soft segment is high and, among others, the flexibility, elongation, bending and elastic recovery performance specifically at low temperatures are poor, and consequently, its application is limited. Furthermore, it is also pointed out that an artificial leather produced using this polyurethane as a raw material has hard touch and uncomfortable “texture” compared with natural leather.
In order to solve these problems, polycarbonate diols having various structures have been proposed.
For example, long-chain dihydroxy compounds such as 1,9-nonanediol, 1,10-decanediol and 1,12-dodecanediol are used for enhancing the flexibility (Patent Documents 1, 2, 3, 4, 5 and 6).